Sensation & Perception

An Introductory Activity Researchers have found that our experiences influence our perceptions Look at the following photographs or drawings and write a short description of each

This is part of the Thematic Apperception Test created by Henry Murray. The TAT is a personality test where the subject writes a theme about what he or she sees, answering questions like “What is happening?” “How will it end?” and “Who are these people?”

What Is Sensation? It occurs when a stimulus activates a sensory receptor A stimulus is measured by the following: size, intensity, duration, wavelength

What Is Perception? The organization of sensory information into meaningful experiences Psychophysics- attempts to describe how we use our senses to detect things in our environment. Ex.- “What is the relationship between color and wavelength?” and “If a light’s intensity changes, how will this affect a person’s perception of its brightness?”

Gustav Fechner Trying to prove that every human, plant, and animal in the world is composed of both matter and “soul.”- failed of course Created experiments that measured sensory data Laid the basis for psychophysics

What Is Meant by a Threshold? Absolute threshold: the smallest amount of a stimuli that a person can reliably detect

Absolute Thresholds For scientists to consider a specific level of a stimulus as an absolute threshold, people have to be able to detect it at least 50 percent of the time Vision: a flame from a single candle 30 miles away Hearing: ticking of a watch 20 feet away Taste: one teaspoon of sugar in two gallons of water Smell: one drop of perfume in a small house Touch: the wing of a bee brushing your cheek

Absolute thresholds differ between species as well: Humans cannot see x-rays or microwaves; dogs can hear a dog whistle but humans can’t; humans hear only about 20 percent of what a dolphin hears; dolphins and bats have a superior sense of hearing; hawks and eagles have extremely sharp vision; and bloodhounds have an acute sense of smell.

Difference Threshold The minimal difference in the magnitude of energy needed for people to distinguish between two stimuli- a “just-noticeable difference.” Weber’s law and experts- the larger or stronger a stimulus the larger the change required for an observer to notice a difference

Sensory Adaptation Senses are most responsive to increases and decreases rather than ongoing unchanging stimulation Our senses have the ability to adapt For example, when you first enter a dark movie theater, you can’t really see anything except blackness. After a while, your eyes adjust to the light and you can pick out seats, faces, etc.

Signal-Detection Theory The study of people’s tendencies to make correct judgments in detecting the presence of stimuli Ex.- The job of a radar operator must be able to detect the difference on his screen between a plane and a flock of birds. Takes into account the many factors that affect detection

The Stroop Effect A B

Processing Stimuli Preattentive process- extracts information automatically and simultaneously when presented with more than one stimulus- Stroop Effect- affects our ability to respond. Attentive process- considers only one stimulus at a time